Engine Electrical Systems

Question 1

What is used as the rectifier to produce direct current in a DC generator?

Answer 1

Brushes and a commutator

Question 2

If the installed ammeter gauge is redlined at 100% of generator or alternator rating, and the regulator does not control current, how is maximum current controlled?

Answer 2

current is controlled by the pilot by not applying loads greater than redline, except for short, intermittent loads

Question 3

If placards or monitoring devices are not practical or desired, what practice protects the battery and electrical system?

Answer 3

The generator is sized so that total continuous load of the electrical system does not exceed 80% of the rated capacity of the generator or alternator

Question 4

When determining maximum continuous electrical load of an aircraft, what defines if the load is intermittent or continuous?

Answer 4

The length of time the system is used. If the component or system is used for less than two minutes, it is considered an intermittent load. More than two minutes is considered continuous load.

Question 5

How is generator output voltage controlled?

Answer 5

By controlling the field current strength through the use of a voltage regulator

Question 6

How are wire sizes represented?

Answer 6

By a numbered gauge size. The smaller wires are represented by larger numbers. The smallest size wire normally used in an aircraft is 22-gauge.

Question 7

What is the maximum slack allowed between the supports of a single wire or bundle installation?

Answer 7

Not over 0.5 inches.

Question 8

Why are wires bonded on powerplant installations?

Answer 8

To provide a current return path for electrical accessories, and to prevent static discharge.

Question 9

How is the voltage of a DC generator controlled?

Answer 9

By varying the field current strength.

Question 10

What is the most common type of alternator used in most aircraft AC systems?

Answer 10

The three phase alternator.

Question 11

How does a voltage regulator control the voltage of an alternator?

Answer 11

By regulating the voltage output of the DC exciter.

Question 12

What does the speed of rotation and number of poles of an alternator determine?

Answer 12

The frequency of the alternator output.

Question 13

What are some of the methods used to maintain 400 hertz alternator output frequency on large turbojet or turbofan engines? (3)

Answer 13

1. Constant speed drives
2. Integrated drive generators
3. Variable- speed constant frequency power systems.

Question 14

Name the major parts of a DC motor.

Answer 14

1. The armature
2. Field
3. Brushes
4. Frame assembly

Question 15

Name the components of a direct cranking electric starter system.

Answer 15

1. An electric motor
2. Reducing gears
3. An automatic engaging and disengaging mechanism

Question 16

Name the three types of DC motors.

Answer 16

1. Series
2. Shunt
3. Compound.

Question 17

What type of DC motor is commonly used for a reciprocating engine starter and why?

Answer 17

A series wound motor is commonly used because it has a high starting torque under heavy loads conditions.

Question 18

What are the operating modes of a turbine engine starter generator?

Answer 18

It operates first as a starter, then as a generator once the engine is running.

Question 19

What is a possible indication when a starter drags?

Answer 19

A dirty or worn starter commutator.

Question 20

Where would wire with high temperature insulation material be used?

Answer 20

When they run close to high temperature areas such as exhaust stacks or heating ducts.

Question 21

What is the size standard for electrical wire used in US manufactured aircraft?

Answer 21

The American wire gauge (AWG).

Question 22

What reduces arcing in the points and also aids the collapsing of the magnetic field in a magneto?

Answer 22

A magneto.

Question 23

How does a magneto produce the high voltage required to fire a spark plug?

DELETE

Answer 23

In the rotation cycle, when the magneto rotor is in the E-gap position, the primary points open, which interrupts the current flow in the primary circuit causing a high rate of flux change in the core, and inducing a pulse of high voltage in the secondary coil.

Question 24

What is the P-lead and how does it function?

Answer 24

The P-lead connects the ignition switch to the primary circuit of the magneto. When the ignition switch is turned off, the P-leads on both of the magnetos are grounded. When the ignition switch is turned to the “LEFT” position, the right magneto is grounded so that only the left magneto operates, and visa versa.

Question 25

What is a magneto timing light used for, and what does it indicate?

Answer 25

It is used for both internal magneto timing and magneto-to-engine timing, and indicates the exact instant the magneto points open.

Question 26

Why are turbine engine igniters generally not susceptible to to carbon fouling?

Answer 26

Because the high energy sparks they produce clean off any deposits on the firing end.

Question 27

What are the three main components of a turbine engine ignition system?

Answer 27

1. Ignition exciters
2. High tension leads
3. Igniters

Question 28

When the engine is operating, what does an ammeter / loadmeter indicate when connected to:

1. Battery positive lead?
2. Generator output lead?

Answer 28

1. When connected to the battery positive lead, the ammeter indicates whether the battery is charging or discharging
2. When connected to the generator output lead, it indicates the current produced by the generator, or the electrical system load.

Question 29

What is done to ensure that each generator shares the load in a multiple generator system?

Answer 29

The generators are paralleled.

Question 30

Where would you find generator rating and performance data?

Answer 30

On the data plate attached to the generator.

Question 31

How can the remaining service life of a starter-generator brushes be determined?

Answer 31

Visually inspecting the amount of wear groove remaining on the brushes.

Question 32

What components of the starter-generator require periodic inspection?

Answer 32

Both commutator and brushes should be inspected for wear beyond operational limits.

Question 33

Between field and armature windings in starter-generator, which ordinarily receive current for operation in the start mode?

Answer 33

Generally, both field and armature receive current for operation in the start mode.

Question 34

What are possible sources of low pressure compressed air used for starting jet transport aircraft equipped with air turbine starters?

Answer 34

1. Ground power unit (GPU)
2. Auxillary power unit (APU)
3. Compressed bleed air from an already running engine

Question 35

When should ignition ideally occur?

Answer 35

A specific number of degrees (as determined by the manufacturer) before the piston reaches top dead center on the compression stroke.

Question 36

Why are dual magnetos used in the engine ignition system?

Answer 36

1. Improve combustion efficiency
2. Provide redundancy for safety

Question 37

Why is magneto timing so important?

Answer 37

The spark plug in a cylinder has to fire at a specific time. If it isn’t timed properly, the engine will run rough or not at all. To produce the required energy for the spark at the required time, the magneto must be in the E-gap position, the breaker points must start to open, and the distributor must be electrically aligned with the particular cylinder. If any of these requirements are not correctly adjusted, the engine will run rough or may not run at all. When preparing a magneto for installation, first the internal timing must be correctly adjusted, then the magneto-to-engine timing is adjusted.

Question 38

What function does a magneto perform?

Answer 38

It produces high voltage that forces a spark to arc across a spark plug gap.

It produces high voltage that creates a spark in the spark plug gap

Question 39

Name the components of a high tension magneto system.

Answer 39

1. A permanent multipole rotating magnet
2. Soft iron core
3. Pole shoes

Question 40

Name three main circuits of a high tension magneto system.

Answer 40

1. Magnetic
2. Primary
3. Secondary.

Question 41

What is an E-gap angle?

Answer 41

It is a point a few degrees beyond the neutral position of a rotating magnet where maximum magnetic field stress exists.